1. Field of the Invention
The present invention relates to a subscriber transmission system for providing telephone service to subscribers located remotely from an exchange office, and more particularly to a subscriber transmission system wherein power supplied to a transmitter of the subscriber side can be reduced when the rate of telephone use is low.
2. Description of the Related Art
A subscriber transmission system is one which concentrates a plurality of subscriber terminals and connects them to an exchange office via optical transmission lines, etc. It is used for the purpose of reduction of transmission loss and construction cost of subscriber lines so that when subscriber terminals are located in places remote from the exchange office, such subscribers can be served by the switching system.
In a thinly populated area, because of the low telephone use rate, it is economically disadvantageous to always supply full electric power to the transmitters of the subscriber side. So, in this case, it is desirable to supply electric power of an amount which corresponds to a specific number of subscribers, so that the amount of consumed electric power may be reduced.
In a conventional subscriber transmission system, since all of the subscriber transmitter-receivers in the transmission apparatus of the subscriber side are connected to subscribers, all of the devices are always supplied with electric power.
However, in the subscriber transmission system, the telephone use rate of the subscribers connected to the subscriber side transmission apparatus is often low. Therefore, there is a problem that supplying all the subscriber transmitter-receivers with electric power results in a waste of electric power supplied in connection with the rate of device use.